DNA encoding a 5-HT 1F receptor and uses thereof

ABSTRACT

This invention provides an isolated nucleic acid molecule encoding a human 5-HT 1F  receptor, an isolated protein which is a human 5-HT 1F  receptor, vectors comprising an isolated nucleic acid molecule encoding a human 5-HT 1F  receptors, mammalian cells comprising such vectors, antibodies directed to the human 5-HT 1F  receptor, nucleic acid probes useful for detecting nucleic acid encoding human 5-HT 1F  receptors, antisense oligonucleotides complementary to any sequences of a nucleic acid molecule which encodes a human 5-HT 1F  receptor, pharmaceutical compounds related to human 5-HT 1F  receptors, and nonhuman transgenic animals which express DNA a normal or a mutant human 5-HT 1F  receptor. This invention further provides methods for determining ligand binding, detecting expression, drug screening, and treatment involving the human 5-HT 1F  receptor.

This application is a continuation of U.S. Ser. No. 08/483,222, filed Jun. 7, 1995, now abandoned which is a continuation of U.S. Ser. No. 08/117,006, filed Aug. 22, 1994, now U.S. Pat. No. 5,639,652, which is the 371 national stage filing of PCT International Application No. PCT/US93/00149, filed Jan. 8, 1993, which is a continuation-in-part of U.S. Ser. No. 07/817,920, filed Jan. 8, 1992, now U.S. Pat. No. 5,360,735.

BACKGROUND OF THE INVENTION

Throughout this application various publications are referenced by partial citations within parentheses. The disclosures of these publications in their entireties are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains.

Since the purification of a pressor substance in blood serum termed serotonin (Rapport et al., 1947) and later identified as 5-hydroxytryptamine (5-HT) (Rapport, 1949), there has been a plethora of reports demonstrating that this indoleamine not only plays a role in the functioning of peripheral tissues but, indeed, performs a key role in the brain as a neurotransmitter. Certainly, the anatomical localization of serotonin and serotonergic neurons in both the peripheral and central nervous systems supports its role in such diverse physiologic and behavioral functions as pain perception, sleep, aggression, sexual activity, hormone secretion, thermoregulation, motor activity, cardiovascular function, food intake and renal regulation (For review see Green, 1985; Osborne and Hamon, 1988; Sanders-Bush, 1988; Peroutka, 1991). Taken together, it appears that serotonin plays an important role in homeostasis and in modulating responsiveness to environmental stimuli. Accordingly, studies demonstrating that abnormalities in the serotonergic system may be associated with disease states has created a drug development effort towards agents which may selectively modulate the function of serotonin (Glennon, 1990).

In relation to the characterization of physiologic or biochemical responses resulting from the release of serotonin are simultaneous investigation examining the receptor sites responsible for the actions elicited by the indoleamine transmitter. Following early in vitro pharmacological assays describing the existence of two different serotonin receptors, designated as D and M, in the guinea pig ileum (Gaddum and Picarelli, 1957), the advent of receptor binding technique in the 1970's has brought to light during the last decade the diversity of 5-HT receptors existing in both the brain and peripheral tissues. Thus, although the concept of D and M receptors has not been invalidated, serotonin receptors not fitting either category have been identified using radioligand methods. To date using this technique, there appears to be four classes of serotonin receptors found in the brain: 5-HT₁, 5-HT₂, 5-HT₃ and, putatively, 5-HT₄ (Peroutka, 1991). Furthermore, 5-HT₁ sites have been subclassified as: 5-HT_(1A), 5-HT_(1B), 5-HT_(1C), 5-HT_(1D) (Hamon et al., 1990) and 5-HT_(1E) (Leonhardt et al., 1989). Although a detailed characterization of the 5-HT_(1F) binding site is lacking, extensive pharmacologic, biochemical and functional properties have clearly shown that the other four subtypes of 5-HT₁ sites are receptors according to classical criteria.

During the last few years, the field of molecular biology has provided an important facet to receptor research by cloning these proteins and allowing more precise characterizations in isolated systems (Hartig et al,1990). This has been accomplished for the 5-HT_(1A) (Fargin et al., 1988), 5-HT_(1C) (Julius et al., 1988), 5-HT_(1D) (Branchek et al., 1990) and 5-HT₂ receptors (Pritchett et al., 1988). Thus, there is no doubt that these binding sites represent “true” functional receptors. Indeed, the pharmacological characterization of serotonin receptors involved in various physiological or biochemical functions is a key component of drug development for the serotonergic system. As one can deduce from the diversity of serotonin binding sites, many targets are available for advancement in selective drug design. The coupling of molecular biological methods to pharmacological characterization particularly for cloned human receptors will open new avenues for pharmaceutical development which has not been previously explored.

This study is a pharmacological characterization of a serotonergic receptor clone with a binding profile different from that of any serotonergic receptor to date. In keeping with the nomenclature presently accepted for serotonin receptors, this novel site will be termed a 5-HT_(1F) receptor based upon the fact that it possesses high affinity for the endogenous neurotransmitter, 5-HT.

SUMMARY OF THE INVENTION

This invention provides an isolated nucleic acid molecule encoding a human 5-HT_(1F) receptor (Seq. I.D. No. 1).

This invention also provides an isolated protein which is a human 5-HT_(1F) receptor (Seq. I.D. Nos. 2, 7).

This invention provides a vector comprising an isolated nucleic acid molecule encoding a human 5-HT_(1F) receptor.

This invention also provides vectors such as plasmids comprising a DNA molecule encoding a human 5-HT_(1F) receptor, adapted for expression in a bacterial cell, a yeast cell, or a mammalian cell which additionally comprise the regulatory elements necessary for expression of the DNA in the bacterial, yeast, or mammalian cells so located relative to the DNA encoding the 5-HT_(1F) receptor as to permit expression thereof.

This invention provides a mammalian cell comprising a DNA molecule encoding a human 5-HT_(1F) receptor.

This invention provides a method for determining whether a ligand not known to be capable of binding to a human 5-HT_(1F) receptor can bind to a human 5-HT_(1F) receptor which comprises contacting a mammalian cell comprising an isolated DNA molecule encoding a human 5-HT_(1F) receptor with the ligand under conditions permitting binding of ligands known to bind to a 5-HT_(1F) receptor, detecting the presence of any of the ligand bound to a human 5-HT_(1F) receptor, and thereby determining whether the ligand binds to a human 5-HT_(1F) receptor.

This invention also provides a method for determining whether a ligand not known to be capable of binding to the human 5-HT_(1F) receptor can functionally activate its activity or prevent the action of a ligand which does so. This comprises contacting a mammalian cell comprising an isolated DNA molecule which encodes a human 5-HT_(1F) receptor with the ligand under conditions permitting the activation of blockade of a functional response, detected by means of bioassay from the mammalian cell such as a second messenger response, and thereby determining whether the ligand activates or prevents the activation of the human 5-HT_(1F) receptor functional output.

This invention further provides a method of screening drugs to identify drugs which specifically interact with, and bind to, the human 5-HT_(1F) receptor on the surface of a cell which comprises contacting a mammalian cell comprising an isolated DNA molecule encoding a human 5-HT_(1F) receptor with a plurality of drugs, determining those drugs which bind to the mammalian cell, and thereby identifying drugs which specifically interact with, and bind to, a human 5-HT_(1F) receptor.

This invention also provides a method of screening drugs to identify drugs which interact with, and activate or block the activation of, the human 5-HT_(1F) receptor on the surface of a cell which comprises contacting the mammalian cell comprising an isolated DNA molecule encoding and expressing a human 5-HT_(1F) receptor with a plurality of drugs, determining those drugs which activate or block the activation of the receptor in the mammalian cell using a bioassay such as a second messenger assays, and thereby identifying drugs which specifically interact with, and activate or block the activation of, a human 5-HT_(1F) receptor.

This invention provides a nucleic acid probe comprising a nucleic acid molecule of at least 15 nucleotides capable of specifically hybridizing with a sequence included within the sequence of a nucleic acid molecule encoding a human 5-HT_(1F) receptor.

This invention also provides a method of detecting expression of the 5-HT_(1F) receptor on the surface of a cell by detecting the presence of mRNA coding for a 5-HT_(1F) receptor which comprises obtaining total mRNA from the cell and contacting the mRNA so obtained with a nucleic acid probe comprising a nucleic acid molecule of at least 15 nucleotides capable of specifically hybridizing with a sequence included within the sequence of a nucleic acid molecule encoding a human 5-HT_(1F) receptor under hybridizing conditions, detecting the presence of mRNA hybridized to the probe, and thereby detecting the expression of the 5-HT_(1F) receptor by the cell.

This invention provides an antisense oligonucleotide having a sequence capable of binding specifically with any sequences of an mRNA molecule which encodes a human 5-HT_(1F) receptor so as to prevent translation of the mRNA molecule.

This invention provides an antibody directed to a human 5-HT_(1F) receptor.

This invention provides a transgenic nonhuman mammal expressing DNA encoding a human 5-HT_(1F) receptor. This invention also provides a transgenic nonhuman mammal expressing DNA encoding a human 5-HT_(1F) receptor so mutated as to be incapable of normal receptor activity, and not expressing native 5-HT_(1F) receptor. This invention further provides a transgenic nonhuman mammal whose genome comprises antisense DNA complementary to DNA encoding a human 5-HT_(1F) receptor so placed as to be transcribed into antisense mRNA which is complementary to mRNA encoding a 5-HT_(1F) receptor and which hybridizes to mRNA encoding a 5-HT_(1F) receptor thereby reducing its translation.

This invention provides a method of determining the physiological effects of expressing varying levels of human 5-HT_(1F) receptors which comprises producing a transgenic nonhuman animal whose levels of human 5-HT_(1F) receptor expression are varied by use of an inducible promoter which regulates human 5-HT_(1F) receptor expression.

This invention also provides a method of determining the physiological effects of expressing varying levels of human 5-HT_(1F) receptors which comprises producing a panel of transgenic nonhuman animals each expressing a different amount of human 5-HT_(1F) receptor.

This invention provides a method for diagnosing a predisposition to a disorder associated with the expression of a specific human 5-HT_(1F) receptor allele which comprises: a. obtaining DNA of subjects suffering from the disorder; b. performing a restriction digest of the DNA with a panel of restriction enzymes; c. electrophoretically separating the resulting DNA fragments on a sizing gel; d. contacting the resulting gel with a nucleic acid probe capable of specifically hybridizing to DNA encoding a human 5-HT_(1F) receptor and labelled with a detectable marker; e. detecting labelled bands which have hybridized to the DNA encoding a human 5-HT_(1F) receptor labelled with a detectable marker to create a unique band pattern specific to the DNA of subjects suffering from the disorder; f. preparing DNA obtained for diagnosis by steps a-e; and g. comparing the unique band pattern specific to the DNA of subjects suffering from the disorder from step e and the DNA obtained for diagnosis from step f to determine whether the patterns are the same or different and to diagnose thereby predisposition to the disorder if the patterns are the same.

This invention provides a method of preparing the isolated 5-HT_(1F) receptor which comprises inducing cells to express 5-HT_(1F) receptor, recovering the receptor from the resulting cells and purifying the receptor so recovered.

This invention also provides a method of preparing the isolated 5-HT_(1F) receptor which comprises inserting nucleic acid encoding 5-HT_(1F) receptor in a suitable vector, inserting the resulting vector in a suitable host cell, recovering the receptor produced by the resulting cell, and purifying the receptor so recovered.

This invention provides an antisense oligonucleotide having a sequence capable of binding specifically with any sequences of an mRNA molecule which encodes a receptor so as to prevent translation of the mRNA molecule.

This invention also provides a transgenic nonhuman mammal expressing DNA encoding a receptor.

This invention further provides a transgenic nonhuman mammal expressing DNA encoding a receptor so mutated as to be incapable of normal receptor activity, and not expressing native receptor.

This invention also provides a method of determining the physiological effects of expressing varying levels of a receptor which comprises producing a transgenic nonhuman animal whose levels of receptor expression are varied by use of an inducible promoter which regulates receptor expression.

This invention also provides a method of determining the physiological effects of expressing varying levels of a receptor which comprises producing a panel of transgenic nonhuman animals each expressing a different amount of the receptor.

This invention further provides a transgenic nonhuman mammal whose genome comprises antisense DNA complementary to DNA encoding a receptor so placed as to be transcribed into antisense mRNA which is complementary to mRNA encoding the receptor and which hybridizes to mRNA encoding the receptor thereby preventing its translation.

This invention provides a method for determining whether a ligand not known to be capable of binding to a receptor can bind to a receptor which comprises contacting a mammalian cell comprising an isolated DNA molecule encoding the receptor with the ligand under conditions permitting binding of ligands known to bind to a receptor, detecting the presence of any of the ligand bound to the receptor, and thereby determining whether the ligand binds to the receptor.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. (FIGS. 1A-1F) Nucleotide and deduced amino acid sequence of gene 5-HT_(1F) (Seq. I.D. Nos. 1, 2, and 7).

Numbers above the nucleotide sequence indicate nucleotide position. DNA sequences was determined by the chain termination method of Sanger, et al., on denatured double-stranded plasmid templates using the enzyme Sequenase. Deduced amino acid sequence (single letter code) of a long open reading frame is shown.

FIG. 2. (FIGS. 2A-2D) Comparison of the human 5-HT_(1F) receptor primary structures with other serotonin receptors (Seq. I.D. Nos.: 5-HT_(1A)- 3; 5-HT_(1C)- 4; 5-HT_(1Dα)- 5; 5-HT_(1Dβ)- 6; 5-HT_(1F)- 7; 5-HT₂- 8).

Amino acid sequences (single letter code) are aligned to optimize homology. The putative transmembrane spanning domains are indicated by stars and identified by Roman numerals (TM I-VIII).

FIG. 3. 5-HT concentration-effect curves are represented in the absence (.) and in the presence (o) of methiothepin (1.0 μM). Data were normalized to 100% relative to forskolin-stimulated values in the absence of agonist to derive values of E_(max) and E₅₀. The antagonist K_(b) was estimated by method of Furchgott (32): K_(b)=(Dose of antagonist)/((E₅₀ in the presence of antagonist/control E₅₀) −1).

FIG. 4. Human tissue distribution of RNA coding for 5-HT_(1F) receptor gene. Total RNA was converted to single-stranded cDNA by random-priming with reverse transcriptase. cDNAs were amplified by PCR using 5-HT_(1F) specific PCR primers. PCR products were run on a 1.5% agarose gel, blotted onto nylon membranes and hybridized to internal gene-specific oligonucleotides and washed under high stringency. Positive represent gene-specific recombinant plasmids; dH₂O served as a negative control. PCR amplification and Southern blotting of RNA samples not treated with reverse transcriptase were negative.

FIG. 5: 5-HT_(1F) receptor mRNA in the guinea pig brain coronal sections. A. An antisense oligonucleotide probe (4,5 loop) was used. An identical pattern was observed with the 5′ untranslated probe (not illustrated). Hybridization densities are high in layer V of cerebral cortex (V), and in CA1-CA3 of the hippocampus (HC). B. Control contralateral hemisphere of an adjacent section to that in A. No hybridization was seen using a sense probe of identical specific activity. C. Section hybridized with the antisense probe. The dorsal raphe (DR) is densely labeled. D. At high magnification, hybridization (antisense probe) is detected in layer V of sensorimotor cortex. Arrowheads indicate heavily labeled pyramidal cells. E. As in D, through the dorsal raphe. Arrowheads indicate large, heavily labeled neurons. Magnification in panels D and E=X270.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the 5-HT receptor family is defined as the group of mammalian proteins that function as receptors for serotonin. A 5-HT receptor subfamily is defined as a subset of proteins belonging to the 5-HT receptor family which are encoded by genes which exhibit homology of greater than 72% or higher with each other in their deduced amino acid sequences within presumed transmembrane regions (linearly contiguous stretches of hydrophobic amino acids, bordered by charged or polar amino acids, that are long enough to form secondary protein structures that span a lipid bilayer). Four human 5-HT receptor subfamilies can be distinguished based on the information presently available: 5-HT₁, 5-HT₂, 5-HT_(3,) and 5-HT₄ (Peroutka, 1991). The 5-HT₂ receptor subfamily contains the human 5-HT₂ receptor. Although no other human members of this family have been described, the rat 5-HT₂ receptor (Pritchett, et al. 1988; Julius, et al. Proc. Natl. Acad. Sci. USA 87:928-932, 1990) and the rat 5-HT_(1C) receptor (Julius, et al. 1988) constitute a rat 5-HT receptor subfamily. The 5-HT₁ subfamily has been subdivided further as: 5-HT_(1A), 5-HT_(1B), 5-HT_(1C), 5-HT_(1D) (Hamon et al., 1990) and 5-HT_(1E) (Leonhardt et al., 1989). The 5-HT_(1A) subfamily contains the human 5-HT_(1A) receptor, also known as G-21 (Fargin, et al. 1988) The 5-HT_(1D) receptor subfamily contains two members, the 5-HT_(1D-1) receptor (also termed 5-HT_(1Dα)) and the 5-HT_(1D-2) receptor (also termed 5-HT_(1Dβ)). The 5-HT_(1F) subfamily contains the human 5-HT_(1F) receptor (also termed clone hl16a). Although this definition differs from the pharmacological definition used earlier, there is significant overlap between the present definition and the pharmacological definition. Members of the 5-HT_(1F) receptor subfamily so described include the 5-HT_(1F) receptor and any other receptors which have a greater than 72% homology to the DNA and amino acid sequence shown in FIG. 1 (Seq. I.D. Nos. 1, 2, and 7) according to the definition of “subfamily”. This invention relates to the discovery of the first member of the human 5-HT_(1F) receptor subfamily.

This invention provides an isolated nucleic acid molecule encoding a human 5-HT_(1F) receptor (Seq. I.D. No. 1). As used herein, the term “isolated nucleic acid molecule” means a nucleic acid molecule that is, a molecule in a form which does not occur in nature. Such a receptor is by definition a member of the 5-HT_(1F) receptor subfamily. Therefore, any receptor which meets the defining criteria given above is a human 5-HT_(1F) receptor. One means of isolating a human 5-HT_(1F) receptor is to probe a human genomic library with a natural or artificially designed DNA probe, using methods well known in the art. DNA probes derived from the human receptor gene 5-HT_(1F) are particularly useful probes for this purpose. DNA and cDNA molecules which encode human 5-HT_(1F) receptors may be used to obtain complementary genomic DNA, cDNA or RNA from human, mammalian or other animal sources, or to isolate related cDNA or genomic clones by the screening of cDNA or genomic libraries, by methods described in more detail below. Transcriptional regulatory elements from the 5′ untranslated region of the isolated clones, and other stability, processing, transcription, translation, and tissue specificity-determining regions from the 3′ and 5′ untranslated regions of the isolated genes are thereby obtained. Examples of a nucleic acid molecule are an RNA, cDNA, or isolated genomic DNA molecule according a human 5-HT_(1F) receptor. Such molecules may have coding sequences substantially the same as the coding sequence shown in FIG. 1. The DNA molecule of FIG. 1 encodes the sequence of the human 5-HT_(1F) receptor gene (Seq. I.D. No. 1).

This invention further provides a cDNA molecule of encoding a human 5-HT_(1F) receptor having a coding sequence substantially the same as the coding sequence shown in FIG. 1 (Seq. I.D. No. 1). This molecule is obtained by the means described above.

This invention also provides an isolated protein which is a human 5-HT_(1F) receptor. As used herein, the term “isolated protein means a protein molecule free of other cellular components. An example of such protein is an isolated protein having substantially the same amino acid sequence as the amino acid sequence shown in FIG. 1 (Seq. I.D. Nos. 2, 7) which is a human 5-HT_(1F) receptor. One means for obtaining isolated 5-HT_(1F) receptor is to express DNA encoding the receptor in a suitable host, such as a bacterial, yeast, or mammalian cell, using methods well known in the art, and recovering the receptor protein after it has been expressed in such a host, again using methods well known in the art. The receptor may also be isolated from cells which express it, in particular from cells which have been transfected with the expression vectors described below in more detail.

This invention provides a vector comprising an isolated nucleic acid molecule such as DNA, RNA, or cDNA encoding a human 5-HT_(1F) receptor. Examples of vectors are viruses such as bacteriophages (such as phage lambda), cosmids, plasmids (such as pUC18, available from Pharmacia, Piscataway, N.J.), and other recombination vectors. Nucleic acid molecules are inserted into vector genomes by methods well known in the art. For example, insert and vector DNA can both be exposed to a restriction enzyme to create complementary ends on both molecules which base pair with each other and are then ligated together with a ligase. Alternatively, linkers can be ligated to the insert DNA which correspond to a restriction site in the vector DNA, which is then digested with the restriction enzyme which cuts at that site. Other means are also available. A specific example of such plasmids is a plasmid comprising cDNA having a coding sequence substantially the same as the coding sequence shown in FIG. 1 and designated clone hl16a.

This invention also provides vectors comprising a DNA molecule encoding a human 5-HT_(1F) receptor, adapted for expression in a bacterial cell, a yeast cell, or a mammalian cell which additionally comprise the regulatory elements necessary for expression of the DNA in the bacterial, yeast, or mammalian cells so located relative to the DNA encoding a human 5-HT_(1F) receptor as to permit expression thereof. DNA having coding sequences substantially the same as the coding sequence shown in FIG. 1 may usefully be inserted into the vectors to express human 5-HT_(1F) receptors. Regulatory elements required for expression include promoter sequences to bind RNA polymerase and transcription initiation sequences for ribosome binding. For example, a bacterial expression vector includes a promoter such as the lac promoter and for transcription initiation the Shine-Dalgarno sequence and the start codon AUG (Maniatis, et al., Molecular Cloning, Cold Spring Harbor Laboratory, 1982). Similarly, a eukaryotic expression vector includes a heterologous or homologous promoter for RNA polymerase II, a downstream polyadenylation signal, the start codon AUG, and a termination codon for detachment of the ribosome. Such vectors may be obtained commercially or assembled from the sequences described by methods well known in the art, for example the methods described above for constructing vectors in general. Expression vectors are useful to produce cells that express the receptor. Certain uses for such cells are described in more detail below.

This invention further provides a plasmid adapted for expression in a bacterial, yeast, or, in particular, a mammalian cell which comprises a DNA molecule encoding a human 5-HT_(1F) receptor and the regulatory elements necessary for expression of the DNA in the bacterial, yeast, or mammalian cell so located relative to the DNA encoding a human 5-HT_(1F) receptor as to permit expression thereof. Some plasmids adapted for expression in a mammalian cell are pSVL (available from Pharmacia, Piscataway, N.J.), pcEXV-3 (Miller J. and Germain R. N., J. Exp. Med. 164:1478 (1986)) and pMO5 (Branchek, T. et al, Mol. Pharm. 38:604-609 (1990)). A specific example of such plasmid is a plasmid adapted for expression in a mammalian cell comprising cDNA having coding sequences substantially the same as the coding sequence shown in FIG. 1 and the regulatory elements necessary for expression of the DNA in the mammalian cell which is designated pMO5-hl16a and deposited under ATCC Accession No. 75175. Those skilled in the art will readily appreciate that numerous plasmids adapted for expression in a mammalian cell which comprise DNA of encoding human 5-HT_(1F) receptors and the regulatory elements necessary to express such DNA in the mammalian cell may be constructed utilizing existing plasmids and adapted as appropriate to contain the regulatory elements necessary to express the DNA in the mammalian cell. The plasmids may be constructed by the methods described above for expression vectors and vectors in general, and by other methods well known in the art.

The deposit discussed supra, and the other deposits discussed herein, were made pursuant to, and in satisfaction of, the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md. 20852.

This invention provides a mammalian cell comprising a DNA molecule encoding a human 5-HT_(1F) receptor, such as a mammalian cell comprising a plasmid adapted for expression in a mammalian cell, which comprises a DNA molecule encoding a human 5-HT_(1F) receptor, the protein encoded thereby is expressed on the cell surface, and the regulatory elements necessary for expression of the DNA in the mammalian cell so located relative to the DNA encoding a human 5-HT_(1F) receptor as to permit expression thereof. Numerous mammalian cells may be used as hosts, including, for example, the mouse fibroblast cell NIH3T3, CHO cells, HeLa cells, Ltk⁻ cells, Y1 cells, etc. A particular example of an Ltk⁻ cell is a cell designated L-5-HT_(1F) and deposited under ATCC Accession No. CRL 10957 and comprises the plasmid designated pMO5-hl16a. Another example is the murine fibroblast cell line designated N-5-HT_(1F) and deposited under ATCC Accession No. CRL 10956. Expression plasmids such as that described supra may be used to transfect mammalian cells by methods well known in the art such as calcium phosphate precipitation, or DNA encoding these 5-HT_(1F) receptors may be otherwise introduced into mammalian cells, e.g., by microinjection, to obtain mammalian cells which comprise DNA, e.g., cDNA or a plasmid, encoding either human 5-HT_(1F) receptor.

This invention provides a method for determining whether a ligand not known to be capable of binding to a human 5-HT_(1F) receptor can bind to a human 5-HT_(1F) receptor which comprises contacting a mammalian cell comprising a DNA molecule encoding a human 5-HT_(1F) receptor, the protein encoded thereby is expressed on the cell surface, with the ligand under conditions permitting binding of ligands known to bind to the 5-HT_(1F) receptor, detecting the presence of any of the ligand bound to the 5-HT_(1F) receptor, and thereby determining whether the ligand binds to the 5-HT_(1F) receptor. This invention also provides a method for determining whether a ligand not known to be capable of binding to the human 5-HT_(1F) receptor can functionally activate its activity or prevent the action of a ligand which does so. This comprises contacting a mammalian cell comprising an isolated DNA molecule which encodes a human 5-HT_(1F) receptor with the ligand under conditions permitting the activation or blockade of a functional response, detected by means of a bioassay from the mammalian cell such as a second messenger response, and thereby determining whether the ligand activates or prevents the activation of the human 5-HT_(1F) receptor functional output. The DNA in the cell may have a coding sequence substantially the same as the coding sequence shown in FIG. 1 preferably, the mammalian cell is nonneuronal in origin. An example of a nonneuronal mammalian cell is an Ltk⁻ cell, in particular the Ltk⁻ cell designated L-5-HT_(1F). Another example of a non-neuronal mammalian cell to be used for functional assays is a murine fibroblast cell line, specifically the NIH3T3 cell designated N-5-HT_(1F). The preferred method for determining whether a ligand is capable of binding to the human 5-HT_(1F) receptor comprises contacting a transfected nonneuronal mammalian cell (i.e. a cell that does not naturally express any type of 5-HT or G-protein coupled receptor, thus will only express such a receptor if it is transfected into the cell) expressing a 5-HT_(1F) receptor on its surface, or contacting a membrane preparation derived from such a transfected cell, with the liquid under conditions which are known to prevail, and thus to be associated with, in vivo binding of the ligands to a 5-HT_(1F) receptor, detecting the presence of any of the ligand being tested bound to the 5-HT_(1F) receptor on the surface of the cell, and thereby determining whether the ligand binds to, activates or prevents the activation on the 5-HT_(1F) receptor. This response system is obtained by transfection of isolated DNA into a suitable host cell containing the desired second messenger system such as phospholnositide hydrolysis, adenylate cyclase, guanylate cyclase or ion channels. Such a host system is isolated from pre-existing cell lines, or can be generated by inserting appropriate components of second messenger systems into existing cell lines. Such a transfection system provides a complete response system for investigation or assay of the activity of human 5-HT_(1F) receptors with ligands as described above. Transfection systems are useful as living cell cultures for competitive binding assays between known or candidate drugs and ligands which bind to the receptor and which are labeled by radioactive, spectroscopic or other reagents. Membrane preparations containing the receptor isolated from transfected cells are also useful for these competitive binding assays. Functional assays of second messenger systems or their sequelae in transfection systems act as assays for binding affinity and efficacy in the activation of receptor function. A transfection system constitutes a “drug discovery system” useful for the identification of natural or synthetic compounds with potential for drug development that can be further modified or used directly as therapeutic compounds to activate or inhibit the natural functions of the human 5-HT_(1F) receptor. The transfection system is also useful for determining the affinity and efficacy of known drugs at the human 5-HT_(1F) receptor sites.

This invention also provides a method of screening drugs to identify drugs which specifically interact with, and bind to, the human 5-HT_(1F) receptor on the surface of a cell which comprises contacting a mammalian cell comprising a DNA molecule encoding a human 5-HT_(1F) receptor on the surface of a cell with a plurality of drugs, determining those drugs which bind to the mammalian cell, and thereby identifying drugs which specifically interact with, and bind to, the human 5-HT_(1F) receptor. This invention also provides a method of screening drugs to identify drugs which interact with, and activate or block the activation of, the human 5-HT_(1F) receptor on the surface of a cell which comprises contacting the mammalian cell comprising an isolated DNA molecule encoding and expressing a human 5-HT_(1F) receptor with a plurality of drugs, determining those drugs which activate or block the activation of the receptor in the mammalian cell using a bioassay such as a second messenger assays, and thereby identifying drugs which specifically interact with, and activate or block the activation of, a human 5-HT_(1F) receptor. The DNA in the cell may have a coding sequence substantially the same as the coding sequence shown in FIG. 1 (Seq. I.D. No. 1). Preferably, the mammalian cell is nonneuronal in origin. An example of a nonneuronal mammalian cell is an Ltk⁻ cell, in particular the Ltk⁻ cell designated L-5-HT_(1F). Another example of a non-neuronal mammalian cell to be used for functional assays is a murine fibroblast cell line, specifically the NIH3T3 cell designated N-5-HT_(1F). Drug candidates are identified by choosing chemical compounds which bind with high affinity to the expressed 5-HT_(1F) receptor protein in transfected cells, using radioligand binding methods well known in the art, examples of which are shown in the binding assays described herein. Drug candidates are also screened for selectivity by identifying compounds which bind with high affinity to one particular 5-HT_(1F) receptor subtype but do not bind with high affinity to any other serotonin receptor subtype or to any other known receptor site. Because selective, high affinity compounds interact primarily with the target 5-HT_(1F) receptor site after administration to the patient, the chances of producing a drug with unwanted side effects are minimized by this approach. This invention provides a pharmaceutical composition comprising a drug identified by the method described above and a pharmaceutically acceptable carrier. As used herein, the term “pharmaceutically acceptable carrier” encompasses any of the standard pharmaceutical carriers, such as a phosphate buffered saline solution, water, and emulsions, such as an oil/water or water/oil emulsion, and various types of wetting agents. Once the candidate drug has been shown to be adequately bio-available following a particular route of administration, for example orally or by injection (adequate therapeutic concentrations must be maintained at the site of action for an adequate period to gain the desired therapeutic benefit), and has been shown to be non-toxic and therapeutically effective in appropriate disease models, the drug may be administered to patients by that route of administration determined to make the drug bio-available, in an appropriate solid or solution formulation, to gain the desired therapeutic benefit.

This invention provides a nucleic acid probe comprising a nucleic acid molecule of at least 15 nucleotides capable of specifically hybridizing with a sequence included within the sequence of a nucleic acid molecule encoding a human 5-HT_(1F) receptor, for example with a coding sequence included within the sequence shown in FIG. 1. As used herein, the phrase “specifically hybridizing” means the ability of a nucleic acid molecule to recognize a nucleic acid sequence complementary to its own and to form double-helical segments through hydrogen bonding between complementary base pairs. Nucleic acid probe technology is well known to those skilled in the art who will readily appreciate that such probes may vary greatly in length and may be labeled with a detectable label, such as a radioisotope or fluorescent dye, to facilitate detection of the probe. Detection of nucleic acid encoding human 5-HT_(1F) receptors is useful as a diagnostic test for any disease process in which levels of expression of the corresponding 5-HT_(1F) receptor is altered. DNA probe molecules are produced by insertion of a DNA molecule which encodes human 5-HT_(1F) receptor or fragments thereof into suitable vectors, such as plasmids or bacteriophages, followed by insertion into suitable bacterial host cells and replication and harvesting of the DNA probes, all using methods well known in the art. For example, the DNA may be extracted from a cell lysate using phenol and ethanol, digested with restriction enzymes corresponding to the insertion sites of the DNA into the vector (discussed above), electrophoresed, and cut out of the resulting gel. An example of such DNA molecule is shown in FIG. 1. The probes are useful for ‘in situ’ hybridization or in order to locate tissues which express this gene family, or for other hybridization assays for the presence of these genes or their mRNA in various biological tissues. In addition, synthesized oligonucleotides (produced by a DNA synthesizer) complementary to the sequence of a DNA molecule which encodes human 5-HT_(1F) receptor of are useful as probes for these genes, for their associated mRNA, or for the isolation of related genes by homology screening of genomic or cDNA libraries, or by the use of amplification techniques such as the Polymerase Chain Reaction. Synthesized oligonucleotides as described may also be used to determine the cellular localization of the mRNA produced by the 5-HT_(1F) gene by in situ hybridization. An example of such an oligonucleotide is: 5′-TCTCACCACTCTCCAAAAGGACTTGGCCATTCACCTCCTCCTTTG-3′ (Seq. I.D. No. 9).

This invention also provides a method of detecting expression of a 5-HT_(1F) receptor on the surface of a cell by detecting the presence of mRNA coding for a 5-HT_(1F) receptor which comprises obtaining total mRNA from the cell using methods well known in the art and contacting the mRNA so obtained with a nucleic acid probe comprising a nucleic acid molecule of at least 15 nucleotides capable of specifically hybridizing with a sequence included within the sequence of a nucleic acid molecule encoding a human 5-HT_(1F) receptor under hybridizing conditions, detecting the presence of mRNA hybridized to the probe, and thereby detecting the expression of the 5-HT_(1F) receptor by the cell. Hybridization of probes to target nucleic acid molecules such as mRNA molecules employs techniques well known in the art. In one possible means of performing this method, nucleic acids are extracted by precipitation from lysed cells and the mRNA is isolated from the extract using a column which binds the poly-A tails of the mRNA molecules. The mRNA is then exposed to radioactively labelled probe on a nitrocellulose membrane, and the probe hybridizes to and thereby labels complementary mRNA sequences. Binding may be detected by autoradiography or scintillation counting. However, other methods for performing these steps are well known to those skilled in the art, and the discussion above is merely an example.

This invention provides an antisense olignucleotide having an sequence capable of binding specifically with any sequences of an mRNA molecule which encodes a human 5-HT_(1F) receptor so as to prevent translation of the mRNA molecule. The antisense oligonucleotide may have a sequence capable of binding specifically with any sequences of the cDNA molecule whose sequence is shown in FIG. 1. As used herein, the phrase “binding specifically” means the ability of a nucleic acid sequence to recognize a nucleic acid sequence complementary to its own and to form double-helical segments through hydrogen bonding between complementary base pairs. A particular example of an antisense oligonucleotide is an antisense oligonucleotide comprising chemical analogues of nucleotides.

This invention also provides a pharmaceutical composition comprising an amount of the oligonucleotide described above effective to reduce expression of a human 5-HT_(1F) receptor by passing through a cell membrane and binding specifically with mRNA encoding a human 5-HT_(1F) receptor in the cell so as to prevent its translation and a pharmaceutically acceptable hydrophobic carrier capable of passing through a cell membrane. The oligonucleotide may be coupled to a substance which inactivates mRNA, such as a ribozyme. The pharmaceutically acceptable hydrophobic carrier capable of passing through cell membranes may also comprise a structure which binds to a receptor specific for a selected cell type and is thereby taken up by cells of the selected cell type. The structure may be part of a protein known to bind a cell-type specific receptor, for example an insulin molecule, which would target pancreatic cells. DNA molecules having coding sequences substantially the same as the coding sequence shown in FIG. 1 may be used as the oligonucleotides of the pharmaceutical composition.

This invention also provides a method of treating abnormalities which are alleviated by reduction of expression of a 5-HT_(1F) receptor which comprises administering to a subject an amount of the pharmaceutical composition described above effective to reduce expression of the 5-HT_(1F) receptor by the subject. This invention further provides a method of treating an abnormal condition related to 5-HT_(1F) receptor activity which comprises administering to a subject an amount of the pharmaceutical composition described above effective to reduce expression of the 5-HT_(1F) receptor by the subject. Several examples of such abnormal conditions are dementia, Parkinson's disease, feeding disorders, pathological anxiety, schizophrenia, or a migraine headache.

Antisense oligonucleotide drugs inhibit translation of mRNA encoding these receptors. Synthetic oligonucleotides, or other antisense chemical structures are designed to bind to mRNA encoding the 5-HT_(1F) receptor and inhibit translation of mRNA and are useful as drugs to inhibit expression of 5-HT_(1F) receptor genes in patients. This invention provides a means to therapeutically alter levels of expression of human 5-HT_(1F) receptors by the use of a synthetic antisense oligonucleotide drug (SAOD) which inhibits translation of mRNA encoding these receptors. Synthetic oligonucleotides, or other antisense chemical structures designed to recognize and selectively bind to mRNA, are constructed to be complementary to portions of the nucleotide sequences shown in FIG. 1 of DNA, RNA or of chemically modified, artificial nucleic acids. The SAOD is designed to be stable in the blood stream for administration to patients by injection, or in laboratory cell culture conditions, for administration to cells removed from the patient. The SAOD is designed to be capable of passing through cell membranes in order to enter the cytoplasm of the cell by virtue of physical and chemical properties of the SAOD which render it capable of passing through cell membranes (e.g. by designing small, hydrophobic SAOD chemical structures) or by virtue of specific transport systems in the cell which recognize and transport the SAOD into the cell. In addition, the SAOD can be designed for administration only to certain selected cell populations by targeting the SAOD to be recognized by specific cellular uptake mechanisms which binds and takes up the SAOD only within certain selected cell populations. For example, the SAOD may be designed to bind to a receptor found only in a certain cell type, as discussed above. The SAOD is also designed to recognize and selectively bind to the target mRNA sequence, which may correspond to a sequence contained within the sequence shown in FIG. 1 by virtue of complementary base pairing to the mRNA. Finally, the SAOD is designed to inactivate the target mRNA sequence by any of three mechanisms: 1) by binding to the target mRNA and thus inducing degradation of the mRNA by intrinsic cellular mechanisms such as RNAse I digestion, 2) by inhibiting translation of the mRNA target by interfering with the binding of translation-regulating factors or of ribosomes, or 3) by inclusion of other chemical structures, such as ribozyme sequences or reactive chemical groups, which either degrade or chemically modify the target mRNA. Synthetic antisense oligonucleotide drugs have been shown to be capable of the properties described above when directed against mRNA targets (J. S. Cohen, Trends in Pharm. Sci. 10, 435 (1989); H. M. Weintraub, Sci. Am. January (1990) p. 40). In addition, coupling of ribozymes to antisense oligonucleotides is a promising strategy for inactivating target mRNA (N. Sarver et al., Science 247, 1222 (1990)). An SAOD serves as an effective therapeutic agent if it is designed to be administered to a patient by injection, or if the patient's target cells are removed, treated with the SAOD in the laboratory, and replaced in the patient. In this manner, an SAOD serves as a therapy to reduce receptor expression in particular target cells of a patient, in any clinical condition which may benefit from reduced expression of 5-HT_(1F) receptors.

This invention provides an antibody directed to the human 5-HT_(1F) receptor, for example a monoclonal antibody directed to an epitope of a human 5-HT_(1F) receptor present on the surface of a cell and having an amino acid sequence substantially the same as an amino acid sequence for a cell surface epitope of the human 5-HT_(1F) receptor included in the amino acid sequence shown in FIG. 1 (Seq. I.D. Nos. 2, 7). Amino acid sequences may be analyzed by methods well known in the art to determine whether they produce hydrophobic or hydrophilic regions in the proteins which they build. In the case of cell membrane proteins, hydrophobic regions are well known to form the part of the protein that is inserted into the lipid bilayer which forms the cell membrane, while hydrophilic regions are located on the cell surface, in an aqueous environment. Therefore antibodies to the hydrophilic amino acid sequences shown in FIG. 1 will bind to a surface epitope of a human 5-HT_(1F) receptor, as described. Antibodies directed to human 5-HT_(1F) receptors may be serum-derived or monoclonal and are prepared using methods well known in the art. For example, monoclonal antibodies are prepared using hybridoma technology by fusing antibody producing B cells from immunized animals with myeloma cells and selecting the resulting hybridoma cell line producing the desired antibody. Cells such as NIH3T3 cells or Ltk⁻ cells may be used as immunogens to raise such an antibody. Alternatively, synthetic peptides may be prepared using commercially available machines and the amino acid sequence shown in FIG. 1. As a still further alternative, DNA, such as a cDNA or a fragment thereof, may be cloned and expressed and the resulting polypeptide recovered and used as an immunogen. These antibodies are useful to detect the presence of human 5-HT_(1F) receptors encoded by the isolated DNA, or to inhibit the function of the receptors in living animals, in humans, or in biological tissues or fluids isolated from animals or humans.

This invention provides a pharmaceutical composition which comprises an amount of an antibody directed to the human 5-HT_(1F) receptor effective to block binding of naturally occurring ligands to the 5-HT_(1F) receptor, and a pharmaceutically acceptable carrier. A monoclonal antibody directed to an epitope of a human 5-HT_(1F) receptor present on the surface of a cell and having an amino acid sequence substantially the same as an amino acid sequence for a cell surface epitope of the human 5-HT_(1F) receptor included in the amino acid sequence shown in FIG. 1 is useful for this purpose.

This invention also provides a method of treating abnormalities which are alleviated by reduction of expression of a human 5-HT_(1F) receptor which comprises administering to a subject an amount of the pharmaceutical composition described above effective to block binding of naturally occurring ligands to the 5-HT_(1F) receptor and thereby alleviate abnormalities resulting from overexpression of a human 5-HT_(1F) receptor. Binding of the antibody to the receptor prevents the receptor from functioning, thereby neutralizing the effects of overexpression. The monoclonal antibodies described above are both useful for this purpose. This invention additionally provides a method of treating an abnormal condition related to an excess of 5-HT_(1F) receptor activity which comprises administering to a subject an amount of the pharmaceutical composition described above effective to block binding of naturally occurring ligands to the 5-HT_(1F) receptor and thereby alleviate the abnormal condition. Some examples of abnormal conditions are dementia, Parkinson's disease, feeding disorders, pathological anxiety, schizophrenia, and a migraine headache.

This invention provides a method of detecting the presence of a 5-HT_(1F) receptor on the surface of a cell which comprises contacting the cell with an antibody directed to the human 5-HT_(1F) receptor, under conditions permitting binding of the antibody to the receptor, detecting the presence of the antibody bound to the cell, and thereby the presence of the human 5-HT_(1F) receptor on the surface of the cell. Such a method is useful for determining whether a given cell is defective in expression of 5-HT_(1F) receptors on the surface of the cell. Bound antibodies are detected by methods well known in the art, for example by binding fluorescent markers to the antibodies and examining the cell sample under a fluorescence microscope to detect fluorescence on a cell indicative of antibody binding. The monoclonal antibodies described above are useful for this purpose.

This invention provides a transgenic nonhuman mammal expressing DNA encoding a human 5-HT_(1F) receptor. This invention also provides a transgenic nonhuman mammal expressing DNA encoding a human 5-HT_(1F) receptor so mutated as to be incapable of normal receptor activity, and not expressing native 5-HT_(1F) receptor. This invention also provides a transgenic nonhuman mammal whose genome comprises antisense DNA complementary to DNA encoding a human 5-HT_(1F) receptor so placed as to be transcribed into antisense mRNA which is complementary to mRNA encoding a 5-HT_(1F) receptor and which hybridizes to mRNA encoding a 5-HT_(1F) receptor thereby reducing its translation. The DNA may additionally comprise an inducible promoter or additionally comprise tissue specific regulatory elements, so that expression can be induced, or restricted to specific cell types. Examples of DNA are DNA or cDNA molecules having a coding sequence substantially the same as the coding sequence shown in FIG. 1 (Seq. I.D. No. 1). An example of a transgenic animal is a transgenic mouse. Examples of tissue specificity-determining regions are the metallothionein promotor (Low, M. J., Lechan, R. M., Hammer, R. E. et al. Science 231:1002-1004 (1986)) and the L7 promotor (Oberdick, J., Smeyne, R. J., Mann, J. R., Jackson, S. and Morgan, J. I. Science 248:223-226 (1990)).

Animal model systems which elucidate the physiological and behavioral roles of human 5-HT_(1F) receptors are produced by creating transgenic animals in which the expression of a 5-HT_(1F) receptor is either increased or decreased, or the amino acid sequence of the expressed 5-HT_(1F) receptor protein is altered, by a variety of techniques. Examples of these techniques include: 1) Insertion of normal or mutant versions of DNA encoding a human 5-HT_(1F) receptor or homologous animal versions of these genes, by microinjection, retroviral infection or other means well known to those skilled in the art, into appropriate fertilized embryos in order to produce a transgenic animal (Hogan B. et al. Manipulating the Mouse Embryo, A Laboratory Manual, Cold Spring Harbor Laboratory (1986)). 2) Homologous recombination (Capecchi M. R. Science 244:1288-1292 (1989); Zimmer, A. and Gruss, P. Nature 338:150-153 (1989)) of mutant or normal, human or animal versions of these genes with the native gene locus in transgenic animals to alter the regulation of expression or the structure of these 5-HT_(1F) receptors. The technique of homologous recombination is well known in the art. It replaces the native gene with the inserted gene and so is useful for producing an animal that cannot express native receptor but does express, for example, an inserted mutant receptor, which has replaced the native receptor in the animal's genome by recombination, resulting in underexpression of the receptor. Microinjection adds genes to the genome, but does not remove them, and so is useful for producing an animal which expresses its own and added receptors, resulting in overexpression of the receptor. One means available for producing a transgenic animal, with a mouse as an example, is as follows: Female mice are mated, and the resulting fertilized eggs are dissected out of their oviducts. The eggs are stored in an appropriate medium such as M2 medium (Hogan B. et al. Manipulating the Mouse Embryo, A Laboratory Manual, Cold Spring Harbor Laboratory (1986)). DNA or cDNA encoding a human 5-HT_(1F) receptor is purified from a vector (such as plasmid pMO5-hl16a described above) by methods well known in the art. Inducible promoters may be fused with the coding region of the DNA to provide an experimental means to regulate expression of the trans-gene. Alternatively or in addition, tissue specific regulatory elements may be fused with the coding region to permit tissue-specific expression of the trans-gene. The DNA, in an appropriately buffered solution, is put into a microinjection needle (which may be made from capillary tubing using a pipet puller) and the egg to be injected is put in a depression slide. The needle is inserted into the pronucleus of the egg, and the DNA solution is injected. The injected egg is then transferred into the oviduct of a pseudopregnant mouse (a mouse stimulated by the appropriate hormones to maintain pregnancy but which is not actually pregnant), where it proceeds to the uterus, implants, and develops to term. As noted above, microinjection is not the only method for inserting DNA into the egg cell, and is used here only for exemplary purposes.

Since the normal action of receptor-specific drugs is to activate or to inhibit the receptor, the transgenic animal model systems described above are useful for testing the biological activity of drugs directed against these 5-HT_(1F) receptors even before such drugs become available. These animal model systems are useful for predicting or evaluating possible therapeutic applications of drugs which activate or inhibit these 5-HT_(1F) receptors by inducing or inhibiting expression of the native or trans-gene and thus increasing or decreasing expression of normal or mutant 5-HT_(1F) receptors in the living animal. Thus, a model system is produced in which the biological activity of drugs directed against these 5-HT_(1F) receptors are evaluated before such drugs become available. The transgenic animals which over or under produce the 5-HT_(1F) receptor indicate by their physiological state whether over or under production of the 5-HT_(1F) receptor is therapeutically useful. It is therefore useful to evaluate drug action based on the transgenic model system. One use is based on the fact that it is well known in the art that a drug such as an antidepressant acts by blocking neurotransmitter uptake, and thereby increases the amount of neurotransmitter in the synaptic cleft. The physiological result of this action is to stimulate the production of less receptor by the affected cells, leading eventually to underexpression. Therefore, an animal which underexpresses receptor is useful as a test system to investigate whether the actions of such drugs which result in under expression are in fact therapeutic. Another use is that if overexpression is found to lead to abnormalities, then a drug which down-regulates or acts as an antagonist to 5-HT_(1F) receptor is indicated as worth developing, and if a promising therapeutic application is uncovered by these animal model systems, activation or inhibition of the 5-HT_(1F) receptor is achieved therapeutically either by producing agonist or antagonist drugs directed against these 5-HT_(1F) receptors or by any method which increases or decreases the expression of these 5-HT_(1F) receptors in man.

This invention provides a method of determining the physiological effects of expressing varying levels of human 5-HT_(1F) receptors which comprises producing a transgenic nonhuman animal whose levels of human 5-HT_(1F) receptor expression are varied by use of an inducible promoter which regulates human 5-HT_(1F) receptor expression. This invention also provides a method of determining the physiological effects of expressing varying levels of human 5-HT_(1F) receptors which comprises producing a panel of transgenic nonhuman animals each expressing a different amount of human 5-HT_(1F) receptor. Such animals may be produced by introducing different amounts of DNA encoding a human 5-HT_(1F) receptor into the oocytes from which the transgenic animals are developed.

This invention also provides a method for identifying a substance capable of alleviating abnormalities resulting from overexpression of a human 5-HT_(1F) receptor comprising administering the substance to a transgenic nonhuman mammal expressing at least one artificially introduced DNA molecule encoding a human 5-HT_(1F) receptor and determining whether the substance alleviates the physical and behavioral abnormalities displayed by the transgenic nonhuman mammal as a result of overexpression of a human 5-HT_(1F) receptor. As used herein, the term “substance” means a compound or composition which may be natural, synthetic, or a product derived from screening. Examples of DNA molecules are DNA or cDNA molecules having a coding sequence substantially the same as the coding sequence shown in FIG. 1.

This invention provides a pharmaceutical composition comprising an amount of the substance described supra effective to alleviate the abnormalities resulting from overexpression of 5-HT_(1F) receptor and a pharmaceutically acceptable carrier.

This invention further provides a method for treating the abnormalities resulting from overexpression of a human 5-HT_(1F) receptor which comprises administering to a subject an amount of the pharmaceutical composition described above effective to alleviate the abnormalities resulting from overexpression of a human 5-HT_(1F) receptor.

This invention provides a method for identifying a substance capable of alleviating the abnormalities resulting from underexpression of a human 5-HT_(1F) receptor comprising administering the substance to the transgenic nonhuman mammal described above which expresses only nonfunctional human 5-HT_(1F) receptor and determining whether the substance alleviates the physical and behavioral abnormalities displayed by the transgenic nonhuman mammal as a result of underexpression of a human 5-HT_(1F) receptor.

This invention also provides a pharmaceutical composition comprising an amount of a substance effective to alleviate abnormalities resulting from underexpression of 5-HT_(1F) receptor and a pharmaceutically acceptable carrier.

This invention further provides a method for treating the abnormalities resulting from underexpression of a human 5-HT_(1F) receptor which comprises administering to a subject an amount of the pharmaceutical composition described above effective to alleviate the abnormalities resulting from underexpression of a human 5-HT_(1F) receptor.

This invention provides a method for diagnosing a predisposition to a disorder associated with the expression of a specific human 5-HT_(1F) receptor allele which comprises: a) obtaining DNA of subjects suffering from the disorder; b) performing a restriction digest of the DNA with a panel of restriction enzymes; c.electrophoretically separating the resulting DNA fragments on a sizing gel; d) contacting the resulting gel with a nucleic acid probe capable of specifically hybridizing to DNA encoding a human 5-HT_(1F) receptor and labelled with a detectable marker; e) detecting labelled bands which have hydridized to the DNA encoding a human 5-HT_(1F) receptor labelled with a detectable marker to create a unique band pattern specific to the DNA of subjects suffering from the disorder; f) preparing DNA obtained for diagnosis by steps a-e; and g) comparing the unique band pattern specific to the DNA of subjects suffering from the disorder from step e and the DNA obtained for diagnosis from step f to determine whether the patterns are the same or different and thereby to diagnose predisposition to the disorder if the patterns are the same. This method may also be used to diagnose a disorder associated with the expression of a specific human 5-HT_(1F) receptor allele.

This invention provides a method of preparing the isolated 5-HT_(1F) receptor which comprises inducing cells to express 5-HT_(1F) receptor, recovering the receptor from the resulting cells, and purifying the receptor so recovered. An example of an isolated 5-HT_(1F) receptor is an isolated protein having substantially the same amino acid sequence as the amino acid sequence shown in FIG. 1 (Seq. I.D. Nos. 2, 7). For example, cells can be induced to express receptors by exposure to substances such as hormones. The cells can then be homogenized and the receptor isolated from the homogenate using an affinity column comprising, for example, serotonin or another substance which is known to bind to the receptor. The resulting fractions can then be purified by contacting them with an ion exchange column, and determining which fraction contains receptor activity or binds anti-receptor antibodies.

This invention provides a method of preparing the isolated 5-HT_(1F) receptor which comprises inserting nucleic acid encoding 5-HT_(1F) receptor in a suitable vector, inserting the resulting vector in a suitable host cell, recovering the receptor produced by the resulting cell, and purifying the receptor so recovered. An example of an isolated 5-HT_(1F) receptor is an isolated protein having substantially the same amino acid sequence as the amino acid sequence shown in FIG. 1. This method for preparing 5-HT_(1F) receptor uses recombinant DNA technology methods well known in the art. For example, isolated nucleic acid encoding 5-HT_(1F) receptor is inserted in a suitable vector, such as an expression vector. A suitable host cell, such as a bacterial cell, or a eukaryotic cell such as a yeast cell, is transfected with the vector. 5-HT_(1F) receptor is isolated from the culture medium by affinity purification or by chromatography or by other methods well known in the art.

This invention provides an antisense oligonucleotide having a sequence capable of binding specifically with any sequences of an mRNA molecule which encodes a receptor so as to prevent translation of the mRNA molecule (Seq. I.D. No. 9).

This invention also provides a transgenic nonhuman mammal expressing DNA encoding a receptor.

This invention further provides a transgenic nonhuman mammal expressing DNA encoding a receptor so mutated as to be incapable of normal receptor activity, and not expressing native receptor.

This invention provides a method of determining the physiological effects of expressing varying levels of a receptor which comprises producing a transgenic nonhuman animal whose levels of receptor expression are varied by use of an inducible promoter which regulates receptor expression.

This invention also provides a method of determining the physiological effects of expressing varying levels of a receptor which comprises producing a panel of transgenic nonhuman animals each expressing a different amount of the receptor.

This invention further provides transgenic nonhuman mammal whose genome comprises antisense DNA complementary to DNA encoding a receptor so placed as to be transcribed into antisense mRNA which is complementary to mRNA encoding the receptor and which hybridizes to mRNA encoding the receptor thereby preventing its translation.

This invention provides a method for determining whether a ligand not known to be capable of binding to a receptor can bind to a receptor which comprises contacting a mammalian cell comprising an isolated DNA molecule encoding the receptor with the ligand under conditions permitting binding of ligands known to bind to a receptor, detecting the presence of any of the ligand bound to the receptor, and thereby determining whether the ligand binds to the receptor.

Applicants have identified individual receptor subtype proteins and have described methods for the identification of pharmacological compounds for therapeutic treatments. Pharmacological compounds which are directed against specific receptor subtypes provide effective new therapies with minimal side effects.

This invention identifies for the first time a new receptor protein, its amino acid sequence, and its human gene. Furthermore, this invention describes a previously unrecognized group of receptors within the definition of a 5-HT_(1F) receptor. The information and experimental tools provided by this discovery are useful to generate new therapeutic agents, and new therapeutic or diagnostic assays for this new receptor protein, its associated mRNA molecule or its associated genomic DNA. The information and experimental tools provided by this discovery will be useful to generate new therapeutic agents, and new therapeutic or diagnostic assays for this new receptor protein, its associated mRNA molecule, or its associated genomic DNA.

Specifically, this invention relates to the first isolated of a human cDNA and genomic clone encoding a 5-HT_(1F) receptor. A new human gene for the receptor identified herein as 5-HT_(1F) has been identified and characterized, and a series of related cDNA and genomic clones have been isolated. In addition, the human 5-HT_(1F) receptor has been expressed in Ltk⁻ cells and NIH3T3 cells by transfecting the cells with the plasmid pMO5-hl16a. The pharmacological binding properties of the protein encoded have been determined, and these binding properties classify this protein as a serotonin 5-HT_(1F) receptor. Mammalian cell lines expressing this human 5-HT_(1F) receptor at the cell surface have been constructed, thus establishing the first well-defined, cultured cell lines with which to study this 5-HT_(1F) receptor.

The invention will be better understood by reference to the Experimental Details which follow, but those skilled in the art will readily appreciate that the specific experiments detailed are only illustrative of the invention as described more fully in the claims which follow thereafter.

EXPERIMENTAL DETAILS Materials and Methods

Polymerase Chain Reaction (PCR): The third (III) and fifth (V) transmembrane domains of the following receptors were aligned and used to synthesize a pair of “degenerate” primers: 5-HT_(1A) (Seq. I.D. No. 3), 5-HT_(1C) (Seq. I.D. No. 4), 5-HT₂ (Seq. I.D. No. 8) and the 5-HT_(1Dα/β) (Seq. I.D. Nos. 5 and 6, respectively) receptors (patent pending). These primers hybridize to opposite strands of target sequences to allow amplification of the region between the corresponding transmembrane domains. That primer which was designed to anneal to transmembrane domain III is designated 3.17 and consists of a mixture of 192 different 31-mers with two inosine nucleotides; the primer which annealed to transmembrane domain V is designated 5.5 and consists of a mixture of 288 different 27-mers with five inosine nucleotides. EcoRI linkers were included at the 5′ end of primer 3.17, to facilitate the subcloning of the amplified cDNA in pBluescript (Stratagene) vectors. 5 μg of poly (A+) RNA from rat brain was reverse transcribed by avian myeloblastosis virus reverse transcriptase (AMV) including 3 μM each of 3.17 and 5.5 primers. The resulting single-stranded cDNA was used in a PCR reaction under the following conditions: 94° C. for 1 minute, 50° C. for 2 minutes and 72° C. for 3 minutes for 40 cycles. Following PCR, 90 μl of the reaction was phenol:chloroform extracted and precipitated; 10 μl was visualized on a gel using ethidium bromide staining. After precipitation the sample was treated with T4 DNA polymerase and digested with EcoRl prior to separation on a 1% agarose gel. The DNA fragment was isolated from the gel, kinased and cloned into pBluescript. Recombinant clones were analyzed by sequencing.

Cloning and Sequencing: A human lymphocyte genomic library (Stratagene) was screened using the rat S51 fragment (obtained by PCR) as a probe. The probe was labeled with ³²P by the method of random priming (Feinberg et al., 1983). Hybridization was performed at 50° C. in a solution containing 50% formamide, 10% dextran sulfate, 5×SSC (1×SSC is 0.15 M sodium chloride, 0.015 M sodium citrate), 1×Denhardt's (0.02% polyvinylpyrrolidone, 0.02% Ficoll, and 0.02% bovine serum albumin), and 200 μg/ml of sonicated salmon sperm DNA. The filters were washed at 50° C. in a 0.1×SSC containing 0.1% sodium dodecyl sulfate (SDS) and exposed at −70° C. to Kodak XAR film in the presence of an intensifying screen. Lambda phage hybridizing to the probe were plaque purified and DNA was prepared for Southern blot analysis (Southern, 1975; Maniatis et al., 1982). For subcloning and further Southern blot analysis DNA was inserted into pUC18 (Pharmacia, Piscataway, N.J.). Nucleotide sequence analysis was done by the Sanger dideoxy nucleotide chain-termination method (Sanger 1977) on denatured double-stranded plasmid templates using Sequenase (U.S. Biochemical Corp. Cleveland, Ohio).

Expression: The entire coding region of clone hl16a was cloned into the eukaryotic expression vector pcEXV-3 (Miller, 1986). Stable cell lines were obtained by cotransfection with the plasmid pcEXV-3 (containing the 5-HT_(1F) receptor gene) and the plasmid pGCcos3neo (containing the aminoglycoside transferase gene) into Ltk⁻ cells or NIH3T3 cells using calcium phosphate (reagents obtained from Specialty Media, Lavellette, N.J.). The cells were grown in a controlled environment (37° C. 5% CO₂) an monolayers in Dulbecco's modified Eagle medium (Gibco, Grand Island, N.Y.) containing 25 mM glucose and supplemented with 10% bovine calf serum, 100 U/ml penicillin G and 100 μg/ml streptomycin sulfate. Stable clones were then selected for resistance to the antibiotic G-418 and harvested membranes were screened for their ability to bind [³H]serotonin.

Membrane Preparation: Membranes were prepared from transfected Ltk⁻ cells which were grown to 100% confluency. The cells were washed twice with phosphate-buffered saline, scraped from the culture dishes into 5 ml of ice-cold phosphate-buffered saline, and centrifuged at 200×g for 5 min at 4°. The pellet was resuspended in 2.5 ml of ice-cold Tris buffer (20 mM Tris-HCl, pH 7.4 at 23°, 5 mM EDTA) and homogenized by a Wheaton tissue grinder. The lysate was subsequently centrifuged at 200×g for 5 min at 4° to pellet large fragments which were discarded. The supernatant was collected and centrifuged at 40,000×g for 20 min at 4°. The pellet resulting from this centrifugation was washed once in ice-cold Tris wash buffer and finally resuspended in a final buffer containing 50 mM Tris-HCl and 0.5 mM EDTA, pH 7.4 at 23°. Membrane preparations were kept on ice and utilized within two hours for the radioligand binding assays. Protein concentrations were determined by the method of Bradford (1976) using bovine serum albumin as the standard.

Radioligand Binding: [³H]5HT binding was performed using slight modifications of the 5-HT_(1D) assay conditions reported by Herrick-Davis and Titeler (1988) with the omission of masking ligands. Radioligand binding studies were achieved at 37° C. in a total volume of 250 μl of buffer (50 mM Tris, 10 mM MgCl₂, 0.2 mM EDTA, 10 μM pargyline, 0.1% ascorbate, pH 7.4 at 37° C.) in 96 well microtiter plates. Saturation studies were conducted using [³H]5-HT at 12 different concentrations ranging from 0.5 nM to 100 nM. Displacement studies were performed using 4.5-5.5 nM [³H]5-HT. The binding profile of drugs in competition experiments was accomplished using 10-12 concentrations of compound. Incubation times were 30 min for both saturation and displacement studies based upon initial investigations which determined equilibrium binding conditions. Nonspecific binding was defined in the presence of 10 μM 5HT. Binding was initiated by the addition of 50 μl membrane homogenates (10-20 μg). The reaction was terminated by rapid filtration through presoaked (0.5% polyethyleneimine filters using 48R Cell Brandel Harvester (Gaithersburg, Md.). Subsequently, filters were washed for 5 sec with ice cold buffer (50 mM Tris HCL, pH 7.4 at 4° C.), dried and placed into vials containing 2.5 ml of Readi-Safe (Beckman, Fullerton, Calif.) and radioactivity was measured using a Beckman LS 5000TA liquid scintillation counter. The efficiency of counting of [³H]5HT averaged between 45-50%. Binding data was analyzed by computer-assisted nonlinear regression analysis (Accufit and Accucomp, Lundon Software, Chagrin Falls, Ohio). IC₅₀ values were converted to K₁ values using the Cheng-Prusoff equation (1973). All experiments were performed in triplicate.

Measurement of cAMP Formation

Transfected NIH3T3 cells (estimated Bmax from one point competition studies=486 fmol/mg of protein) were incubated in DMEM, 5 mM theophylline, 10 mM Hepes (4-[2-Hydroxyethyl]-1-piperazineethanesulfonic acid), 10 μM pargyline, for 20 minutes at 37° C., CO2. Drug dose-effect curves were then conducted by adding 6 different final concentrations of drug, followed immediately by the addition of forskolin (10 μM). Subsequently, the cells were incubated for an additional 10 minutes at 37° C., 5% CO2. The media was aspirated and the reaction terminated by the addition of 100 mM HCl. The plates were stored at 4° C. for 15 minutes and centrifuged for 5 minutes (500×g at 4° C.) to pellet cellular debris. Aliquots of the supernatant fraction were then stored at −20° C. prior to assessment of cAMP formation by radioimmunoassay (cAMP Radioimmunoassay kit, Advanced Magnetics, Cambridge, Mass.).

Tissue Localization Studies. Human tissues (NDRI) were homogenized and total RNA extracted (Sambrook et al., 1989). cDNA was prepared from 5 μg of total RNA with random hexanucleotide primers (500 pmoles) using Superscript reverse transcriptase (BRL) in PCR reaction buffer (Cetus Corp.) containing 1 mM dNTPs, at 42° C. for 1 hr. An aliquot of the first strand cDNA was diluted (1:5) in a 50 μl PCR reaction mixture (200 μM dNTPs final concentration) containing 1.25 U of Taq polymerase and 1 μM of primers from the sense strand (5′TCTATTCTGGAGGCACCAAGGAAC3′) (SEQ ID NO:10) and from the antisense strand (5′TGTTGATGGGTCAGATAAAGACTT3′) (SEQ ID NO:11). The PCR products were run on a 1.5% agarose gel and transferred to charged nylon membrane (2etaProbe, Bio-Rad). Filters were hybridized and washed under high stringency.

In Situ Hybridization. In situ hybridization was performed as described previously (McCabe et al., 1989) using male Hartley guinea pigs (300-350 g). A fragment of the guinea pig 5-HT_(1F) receptor gene was cloned by homology and sequenced. 45-base oligoprobes synthesized to the 4,5 loop and 5′ untranslated regions were 3′ end-labeled with ³⁵S-dATP to a specific activity of 4×10⁹ Ci/mmol. The nucleotide sequences were: 5′GTGATGCTTGATGATGCACTCATCATCTCGGCTTGTCCCCTGGTG 3′ and 5′TAGCAGTTCCTCTGAGGTCAAGTTTTGATCAGAAGAGTTTAAGAA 3′ (SEQ ID NO:13). Sense probes, melting temperature, and RNase pretreatment were used as controls. Sections were exposed to Kodak X-OMAT AR film for 1 week or coated with Kodak NTB-2 emulsion/2% glycerol (1:1) for 2 weeks. Similar experiments were also done on human tissue.

Drugs: [³H]5-HT (specific activity=28 Ci/mmole) was obtained from New England Nuclear, Boston, Mass. All other chemicals were obtained from commercial sources and were of the highest grade known purity available.

Results Cloning of a Novel Gene Encoding a 5HT_(1F) Receptor

Polyadenylated (poly A−) RNA prepared from rat brain was reverse transcribed and the resulting cDNAs were subjected to amplification by PCR with the use of a set of “degenerate” primers. The synthesis of these primers were based on sequences corresponding to the third and fifth transmembrane segments of the current set of available serotonin receptors. The primers were designed to amplify only serotonin specific sequences. This was accomplished, particularly with the transmembrane domain V primer, which was designed to anneal at its 3′ end only to the sequence “AFY(F)IP”. We have determined by sequence analysis that the presence of an alanine (A) rather than a serine (S) in the position immediately amino-terminal to the sequence “FY(F)IP” is an amino acid which can distinguish the closely related adrenergic and dopaminergic receptor families from the serotonergic receptor family. After 30 amplification cycles, agarose gel electrophoresis revealed a clear pattern of cDNA species of approximately 250 base pairs. Individual cDNAs were cloned directly into pBluescript and subjected to sequence analysis. One clone, designated S51, was observed to encode a novel serotonin receptor. We then screened a human genomic placental library with the PCR fragment S51. Isolation of the full-length coding region was obtained from a genomic clone designated hl16a.

Nucleotide Sequence and Deduced Amino Acid Sequence of hl16a

DNA sequence information obtained from clone hl16a is shown in FIG. 1. An open reading frame extending from an ATG start codon at position 1 to a stop codon at position 1098 can encode a protein 366 amino acids in length, having a relative molecular mass (M_(r)) of 41,660. A comparison of this protein sequence with previously characterized neurotransmitter receptors indicates that hl16a encodes a receptor which is a new member of a family of molecules which span the lipid bilayer seven times and couple to guanine nucleotide regulatory proteins (the G protein-coupled receptor family). A variety of structural features which are invariant in this family were present including the aspartic acid residues of transmembrane regions II and III, the DRY sequence at the end of transmembrane region III, and the conserved proline residues of transmembrane regions IV, V, VI and VII (Hartig et al. and references therein), were present in clone hl16a. A comparison of the transmembrane homology of hl16a to the other cloned serotonin receptors is shown if FIG. 2 exhibits the following order of identity: 5-HT_(1Dα)(61%), 5-HT_(1DS) (59%), 5-HT_(1A) (54%), 5-HT_(1C) (44%) and 5-HT₂ (44%).

Receptor Expression in Transfected Mammalian Cells

Saturation analysis of membranes prepared from stably transfected Ltk- cells demonstrated that the receptor expressed was saturable and of high affinity. Scratchard plot analysis by non-linear regression revealed a Kd of 9.2±0.99 nM (mean±S.E.M., n=4) and a B_(max) 4.4=0.36 picomoles/mg of protein (mean±S.E.M., n=4). The percent specific binding determined at the measured Kd value for [³H]5-HT was greater than 85% of total binding. Furthermore, evidence that the receptor is coupled to a G-protein was demonstrated by the ability of Gpp(NH)p, a non-hydrolyzable analog of GTP, to inhibit the specific binding of [³H]5-HT (IC₅₀=243±115, n_(H)=0.71±0.08, I_(max)=55.6±3.2%; means ±S.E.M., n=3). Additional data demonstrating that this coupling to a G-protein is functionally relevant is provided below.

Pharmacological analysis of the receptor was accomplished by testing the ability of drugs from different chemical classes to displace [3H]5-HT specific binding (Table 1). Of the compounds investigated, 5-HT possessed the highest affinity which according to the classification system of Peroutka and Snyder (1979) makes this site a member of the 5-HT₁ class. Interestingly, 5-CT possessed low affinity and, thus, discriminates this receptor from that of the 5-HT_(1D) receptor as well as other members of this class. The one exception appears to be the recently cloned 5-HT_(1E) receptor which also has low affinity for 5-CT (U.S. Ser. No. 803,626, filed Dec. 2, 1991, copending). Various ergoline compounds also bound with high affinity including methylergonovine and methysergide. Excluding 1-napthylpiperazine (K1=54), piperazine derivatives had low affinity. Interestingly, the rauwolfia alkaloids, rauwolscine and yohimbine, which are alpha-2 adrenergic antagonists had fair affinity for this serotonergic receptor. Furthermore, miscellaneous serotonergic agents that possess high affinity for various receptors within the serotonin family including ketanserin (5-HT₂), 8-OH-DPAT (5-HT_(1A)), DOI (5-HT_(1C)/5-HT₂), spiperone (5-HT_(1A)/5-HT₂), pindolol (5-HT_(1A)/5-HT_(1B), and zacopride (5-HT₃) had very poor affinity. Taken together, the pharmacological profile of the 5-HT_(1F) receptor is unique and contrasts to that of other known serotonin receptors. Interestingly, the agonist rank order of potency (but not antagonist profile) matches one described for large motorneurons in the spinal cord evaluated electrophysiologically (Connel et al., 1989). Accordingly, the probability of developing selective drugs for this receptor subtype is increased. The functional 5-HT response (1 μM) was completely blocked by the nonselective antagonist methiothepin (10 μM). This antagonism was surmountable (FIG. 3), indicating probable competitive antagonism. The dose shift produced by methiothepin yielded an apparent K_(D) of 438±14 nM, consistent with the K₁ for this compound (Table 1). No direct effect of methiothepin was observed. No other compound tested in this study was an antagonist. In addition, no evidence for coupling of this receptor to PI turnover was detected at a dose of 10 μM 5-HT.

TABLE 1 Ki (nM) values of various drugs for the inhibition of [³H]5-HT specific binding to clonal 5-HT_(1F) cell membranes. Binding assays were performed with 4.5- 5.5 nM of [³H]5-HT and 10-12 different concentrations of each inhibitory drug. K1 values were calculated from the IC₅₀ values using the Cheng-Prusoff equation. Each value is the mean ± S.E.M. of 2-4 independent determinations. COMPOUND K1 (nM) 5-HT 10.3 ± 2.0  Sumatriptan 23.0 ± 11.0 Ergonovine 31.0 ± 1.5  Methylergonovine 31.0 ± 11.0 Methysergide 34.0 ± 4.9  5-Methoxy-N,N-DMT 37.5 ± 1.5  1-Napthylpiperazine 54.0 ± 3.8  Yohimbine 92.0 ± 11.0 Ergotamine 171 ± 28  α-Methyl-5-HT 184 ± 35  NAN 190 203 ± 13  Dihydroergotamine 276 ± 49  Metergoline 341 ± 71  2-Methyl-5-HT 413 ± 5.6  Methiothepin 652 ± 41  5-CT 717 ± 71  TFMPP 1,002 ± 85   5-MT 1,116 ± 197   SCH 23390 1,492 ± 165   5-Benzoxytryptamine 1,495 ± 893   DP-5-CT 1,613 ± 817   DOI 1,739 ± 84   8-OH-DPAT 1,772 ± 38   5-Fluorotryptamine 1,805 ± 220   mCPP 2,020 ± 36   Tryptamine 2,409 ± 103   Quipanzine 4,668 ± 814   Ritanserin 3,521 ± 86   Propanolol 8,709 ± 97   Ketanserin >10,000 Spiperone >10,000 Zacopride >10,000 Pindolol >10,000 Mesulergine >10,000 Harmaline >10,000 Melatonin >10,000

cAMP Assay

Additional supporting evidence that the 5-HT1F receptor is functionally coupled to a G-protein was obtained by testing the ability of 5-HT as well as other representative serotonergic drugs to inhibit forskolin stimulated cAMP production in NIH3T3 cells transfected with the 5-HT1F receptor. The endogenous indoleamine, 5-HT, produced a concentration-related decrease in forskolin-stimulated cAMP production with an EC50 of 7.1 ±1.3 nM (n=4). The maximum inhibition of cAMP production by 5-HT was 67±5.4%. Additionally, the serotonergic compounds 1-napthylpiperazine and lysergol inhibited forskolin-stimulated cAMP production with EC50 value of 4.5±0.2 nM and 8.8±4.3 nM (n=2), respectively.

Receptor Localization Studies

Expression of the 5-HT_(1F) transcripts was analyzed from PCR-northern blots and in situ hybridization studies. By PCR, we detected 5-HT_(1F) receptor mRNA in the human brain, uterus (endometrium and myometrium) and mesentery (FIG. 4) but not in kidney, liver, spleen, heart, pancreas, or testes. In in situ hybridization experiments, we observed 5-HT_(1F) transcripts in lamina V of frontal cortex (FIG. 5A) in large pyramidal cells (FIG. 5D). Moderate labeling was also detected over layer VI non-pyramidal neurons. In both layer V and layer VI, the labeling was most evident in dorsal sensorimotor neocortex, and in cingulate and retrosplenal cortices (FIG. 5C). The pyramidal cells in the piriform cortex were heavily labeled as were large neurons in the raphe nuclei (FIG. 5E). Hippocampal pyramidal cells in CA1-CA3 were moderately labeled, as were the granule cells in the dentate gyrus, and some neurons in the nucleus of the solitary tract. Little labeling was found in the thalamus and hypothalamus. Significant labelling was also found in the large motoneurons of the ventral horn of the spinal cord. The localization in the human was found to be in good concordance with that observed in the guinea pig.

Discussion

The deduced amino acid sequence of hl16a was analyzed to uncover relationships between it and the other cloned serotonin receptor sequences. Although the homology within the membrane spanning domains was greatest with the 5-HT_(1Dα)receptor (FIG. 2), the nature of this newly cloned receptor could not be clearly predicted. The rational for this ambiguity is the interpretation of the transmembrane domain homology (approximately 60%) to the 5-HT_(1Dα)and 5-HT_(1Dβ)receptor subfamily. Closely related members of a “subfamily” of serotonin receptors (i.e. “subtypes”) generally share a common transmitter and also have similar pharmacological profiles and physiological roles (for example, 5-HT₂ and 5-HT_(1C) or 5-HT_(1Dα)and 5-HT_(1Dβ)). Such “subtypes” display an amino acid identity of approximately 75-80% in their transmembrane domains. Serotonin receptors which are not members of the same “subfamily”, but are members of the serotonin “family” (in which the receptors use the same neurotransmitter; i.e. 5-HT₂ and 5-HT_(1Dα)) generally show much lower transmembrane homology (approximately 45%). Such transmembrane amino acid homologies can, therefore, give insight into the relationship between receptors and be used as predictors of receptor pharmacology. According to this type of analysis, although the newly cloned receptor appears to be more related to the 5-HT_(1D) subfamily, it is likely to be in a subfamily distinct from all the other serotonin receptors. Interestingly, the transmembrane homology between the 5HT_(1E) (Levy et al., 1992; McAllister et al. 1992; Zgombick et al., 1992) and 5-HT_(1F) (Amlaiky et al., 1992; Adham et al., in press) receptors is 72%. It is therefore possible that these receptors maybe “subtypes”, rather than members of distinct “subfamilies”.

The present pharmacological evidence substantiates the existence of a novel serotonin receptor in the human brain and peripheral tissues. Comparison of the binding affinities for various drugs observed in native membranes for other known serotonergic receptors (see Hoyer, 1989) to that of the 5-HT_(1F) receptor demonstrates that the pharmacological profile does not fit any known receptor to date. The cloning of the 5-HT_(1F) site will now allow more extensive investigations into the nature of this unique serotonergic receptor.

The structure-activity relationships observed in the present study suggest that there are important requirements for high affinity binding to the 5-HT_(1F) receptor. Substitution or removal of the 5-hydroxy group on serotonin significantly decreases the affinity for the receptor (egs., tryptamine, 5-methoxytryptamine and 5-carboxyamidotryptamine). Additionally, α-methylation and 2-methylation of 5-HT lowers its affinity by 20 and 40 fold, respectively, for the 5-HT_(1F) site. In contrast to these substitutions, N,N-dimethylation of the aliphatic side chain of the indole ring increases the affinity approximately 20 fold (unpublished observations). Interestingly, 5-methoxy-N,N-dimethyltryptamine which possesses both a 5-hydroxy substitution as well as a N,N-dimethylation has an affinity much higher than the other 5-substituted tryptamine derivatives. Basic structural requirements of the ergoline derivatives demonstrate that N-methylation of the indole ring does not decrease affinity as does bulky substitutions. Furthermore, piperazine derivatives are not bound at high affinity.

Notably, the application of the human 5-HT_(1F) receptor clone to pharmaceutical research can lead to new drug design and development. In this regard, it is important to point out that the affinities of sumatriptan, methylergonovine and methysergide for this receptor suggest that this site may be involved in the control of migraine headaches. Certainly, these compounds have had success in the clinic for the treatment of this debilitating disorder (Sleight et al., 1990). Notably, however, it has been thought that the action of these compounds is mediated at 5-HT1D receptors for sumatriptan and 5-HT2 receptors for methysergide. Interestingly, methylergonovine may be an active metabolite of methysergide which can be responsible for some of the therapeutic antimigraine effects of methysergide. This novel site with affinity for these agents would now suggest that there is one serotonergic receptor which may be responsible for both the pathogenesis and, accordingly, the pharmacological treatment. Importantly, the agents prescribed for migraine are not selective for any one particular serotonin receptor and, thus, the physiological significance of drugs acting at one specific site remains controversial (Humphrey P. P. A. et al., 1990). The notion that the 5-HT_(1F) receptor is involved in migraine may be supported by evidence demonstrating that metergoline which has high affinity for the 5-HT_(1D) receptor does not block the effects of sumatriptan in the dog saphenous vein (Sumner and Humphrey, 1990) inferring that this vascular model may contain the novel 5-HT_(1F) site. Furthermore, this data can support the idea that sumatriptan acts at 5-HT_(1F) receptors as an anti-migraine drug. Localization of transcripts for the 5-HT_(1F) receptor in the spinal trigeminal nucleus by in situ hybridization strongly supports this contention (Buzzi et al.,1990, 1991; Moskowitz et al., 1992). The potential of the 5-HT_(1F) receptor as a novel target for migraine where selective drugs may be developed is an exciting possibility which needs to be explored.

Further insight into potential therapeutic significance of the 5-HT1F receptor has been obtained through localization studies using PCR and in situ hybridization. Localization of transcripts for this receptor indicates a relatively selective tissue distribution. Of tissues reported here, the 5-HT_(1F) receptor was only detected in a few including the brain, uterus, and mesentery. The possible role of this receptor in uterine or vascular function is intriguing. Future studies defining the specific cell type(s) in these tissues which express the receptor may provide insight into its function in the periphery. Possibilities for therapeutic benefit include dysmenorrhea and labor induction uterus) and hypertension (vascular components of mesentery) and obesity (adipose components). In the brain, the expression of the 5-HT1F receptor had a limited distribution compared to that of other serotonin receptors. In the neocortex, labelling of layer V pyramidal neurons may indicate a functional role for the 5-HT_(1F) receptor protein in the integration of sensorimotor (somatodendritic; frontal cortex) or afferent information associated with limbic functions (somatodendritic; cingulate/retrosplenial cortex), or in spinal cord processes (axonal). Intense labeling was detected in the large motoneurons of the ventral horn of the spinal cord. Strong labeling was also detected in hippocampal pyramidal cells, in several thalamic nuclei, and in the dorsal raphe. The detection of transcripts for this gene in the dorsal raphe nucleus indicates a possible role as an autoreceptor. Autoreceptor function opens the possibility that the 5-HT_(1F) receptor could be involved in any or all of the known actions of serotonin including therapeutic potential in anxiety, depression, sleep disorders including jet lag, appetite control, sexual dysfunction, gastrointestinal motility including irritable bowel disease, and cardiovascular regulation. In addition, localization to the large motoneurons indicates a possible role in spasticity and other disorders of movement.

Another consideration for therapeutic application of this site may be related to the treatment of feeding disorders such as obesity, bulimea nervosa and/or anorexia nervosa. The involvement of serotonin and feeding behavior has received much attention during the last decade. It is now known that many of the identified and well-characterized serotonergic receptors are capable of modulating feeding (Blundell and Lawton, 1990). Notably, serotonin uptake blockers which have been used to treat feeding disorders act nonselectively and as such have side-effect potential (Jimerson et al., 1990). The fact that the 5-HT_(1F) receptor has been cloned from both peripheral and central sites, and has been localized by both PCR and by in situ hybridization, suggests from an anatomical standpoint that it can be found in strategic locations where feeding may be altered. Although many different serotonergic receptors are involved in feeding, the search for the one site that can be exploited for selective drug development has yet to be found. There is no doubt that interest exists in finding drugs that interact with the serotonin system for the treatment of feeding disorders (Cooper, 1989).

Overall, the 5-HT_(1F) receptor can be an important site stimulated by nonselectively blocking serotonin uptake as is accomplished with certain antidepressants. In regard to this, serotonin uptake blockers are effective in treating neuropsychiatric disorders such as depression and obsessive-compulsive illness (Asberg et al., 1986; Sleight et al., 1990; Insel et al., 1985). However, these agents have side effects and, in fact, the mechanism of action for these compounds are not linked to any particular serotonergic receptor. The possibility that agents selective for the 5-HT_(1F) receptor may have clinical utility as antidepressants, for example, without the side effects attributed to current treatment modalities can have significant implications for drug therapy. The localization of the 5-HT1F receptor in the raphe nuclei, and therefore its potential role as an autoreceptor, further supports the role for this receptor subtype in depression.

In summary, the pharmacological profile of the cloned human 5-HT_(1F) receptor is unique and contrasts to other known serotonergic receptors. The utility of this site expressed in a cellular system and, thus, isolated for study will create excellent opportunities in drug development directed towards a novel serotonergic receptor that may have wide-range implications for drug therapy. Ultimately, indepth investigations into the localization of this receptor in brain and peripheral tissue will target new sites that may lead to functional roles of the serotonergic receptor. Indeed, the potential therapeutic applications may extend to neuropsychiatric disorders including depression, anxiety, schizophrenia, dementia and obsessive-compulsive illness as well as obesity and migraine.

Additionally, the localization of the 5-HT_(1F) receptor in the spinal cord suggests possible roles for this subtype ion analgesia as well as spasticity. The clear evidence of involvement of this receptor in the ventral horn further supports the possible role in motor control. Interestingly, the agonist profile of the 5-HT_(1F) receptor matches that reported for large motoneurons of the spinal cord measured electrophysiologically (Connel et al., 1989). In addition, the presence of the 5-HT_(1F) receptor in the mesentery, at major resistance bed of the vascular tree, indicated a role in the control of blood pressure. A detailed accounting of the localization and therapeutic potential is presented in Table II.

TABLE II Summary of the localization of mRNA for the 5-HT_(1F) receptor in the guinea pig and human CNS. Experiments were performed as described (methods). Each experiment was replicated 2- 3 times. Potential therapeutic roles anticipated base or these data are indicated. LOCALIZATION OF HUMAN 5HT_(1F) mRNA* THERAPEUTIC AREAS PROJECTIONS RELEVANCE FRONTAL CORTEX Main projections to Potential application striatum, dorsal for the development thalamus, and of treatments for superior colliculus. schizophrenia and mood disorders. CAUDATE Primary projections Potential treatment NUCLEUS to globus pallidus, of any basal ganglia substantia nigra. disorder, including Parkinson's disease, Huntington's chorea, or tardive dyskinesia. HIPPOCAMPAL Pyramidal neurons Primary locus for FORMATION project mainly treatment of memory within the disorders, e.g. hippocampus, and Alzheimer's disease also to the septum. or for cognitive enhancement in people with learning disabilities. Also possible treatment for temporal lobe epilepsy. AMYGDALA Cells in amygdala Wide range of have widespread potential projections to applications. These cortex, hippocampus, include treatment of basal ganglia, autonomic hypothalamus, and dysfunctions such as brainstem autonomic cardiac arrhythmias centers. and non-adaptive response to environmental stressors. Also potential treatment of mood disorders, such as bipolar syndrome. HYPOGLOSSAL Main projections to Treatment of verbal NUCLEUS somatic skeletal apraxia. musculature of the tongue. DORSAL Principal May have some EFFERENT projections are to application to the NUCLEUS OF THE the parasympathetic treatment of stress- VAGUS ganglia and related ulcers and abdominal viscera. iritable bowel disease. NUCLEUS OF THE Main projections are Varied potential SOLITARY TRACT to thalamus, applications, with amygdala, regulation of cardio- rostroventral vascular function the medulla, and the Al most prominent, e.g. noradrenergic cell an anti-hypertensive. group of the dorsal medulla. GRACILE Provides innervation Potential NUCLEUS of lumbosacral applications for the spinal cord. treatment of dermatitis, or pain associated with itching. CUNEATE Provides innervation Potential NUCLEUS of cervical spinal applications for the cord. treatment of dermatitis, or pain associated with itching. SPINAL Main projections are Potential treatment TRIGEMINAL to the contralateral of migraine NUCLEUS ventrobasal headaches, and other thalamus, the pain syndromes such posterior thalamic as trigeminal n., the zona neuralgia. incerta, the superior colliculus, and the motor nuclei of trigeminal. OLIVARY Primary projections Treatment of ataxia COMPLEX are to the associated with cerebellum. olivopontocerebellar atrophy, or tremors accompanying some neurodegenerative diseases RETICULAR Projections to the Involvement in FORMATION intra-laminar and cardiac pressor and dorsomedial n. of depressor responses thalamus, the suggests a role in hypothalamus, blood pressure supramammillary and regulation and lateral mammillary possibly a treatment nuclei, theseptum, for hypertension. the diagonal band, Also possible spinal cord, application for the cerebellum, treatment of urinary brainstem autonomic retention disorders, nuclei. and in the management of pain. MEDIAL Projections to Treatment of motion VESTIBULAR oculomotor complex sickness. NUCLEUS and cervical spinal cord motor neurons. CEREBELLAR Projections only to Potential treatment PURKINJE CELLS deep cerebellar of movement nuclei. disorders, particularly those involving planned movements, or those involving abnormalities of gait or stance. SPINAL CORD Ascending dorsal Primary site for VENTRAL HORN horn projections to treatment of pain, thalamus, brainstem and for possible reticular formation anesthetic and central gray. applications. Also Ventral horn possible therapies projections to for spasticity and skeletal and/or movement disorders. smooth muscle. ANTERIOR Widespread Treatment of OLFACTORY projections to olfactory disorders NUCLEI and brain olfactory (dysosmais) PIRIFORM centers, to limbic associated with many CORTEX system, neurological hypothalamus, syndromes. thalamus, and striatum. LAYER V of Cells of layer V Enhancement of memory NEOCORTEX project primarily for motor tasks, to other cortical particularly in areas, and to certain amnestic basal ganglia. syndromes, e.g. Alzheimer's disease. CAUDATE- Medium spiny Potential treatment PUTAMEN and neurons project to of any basal ganglia NUCLEUS globus pallidus, disorder, including ACCUMBENS entopeduncular n., Parkinson's disease, and substantia Huntington's chorea, nigra. or tardive dyskinesia. AMYGDALA Cells in amygdala Wide range of have widespread potential projections to applications. These cortex, include treatment of hippocampus, basal autonomic ganglia, dysfunctions such as hypothalamus, and cardiac arrhythmias brainstem and non-adaptive autonomic centers. response to environmental stressors. Also potential treatment of mood disorders, such as bipolar syndrome. HIPPOCAMPUS Pyramidal neurons Primary locus for project mainly treatment of memory within the disorders, e.g. hippocampus, and Alzheimer's disease also to the or for cognitive septum. enhancement in people with learning disabilities. Also possible treatment for temporal lobe epilepsy. DORSAL RAPHE Extensive Treatment of pain projections to syndromes, including cerebral cortex, migraine headache. frontal striatum, Involvement of raphe limbic structures, in general olfactory arousal/attentional tubercle, central processes makes this gray, hippocampus, a possible target for and spinal cord. treatment of attentional dysfunctions, such as those observed in Alzheimer's disease, or in developmental disabilities. Potential application in the treatment of depression. PONTINE Major projection Potential treatment NUCLEI is to the of movement cerebellar cortex. disorders, particularly planned movement, and gait disorders such as Friedrich's ataxia. INFERIOR Major obligatory COLLICULUS synaptic station in ascending auditory pathway. TRIGEMINAL Main projections Potential treatment NUCLEAR are to the of migraine COMPLEX contralateral headaches, and other ventrobasal pain syndromes such thalamus, the as trigeminal posterior thalamic neuralgia. n., the zona incerta, the superior colliculus, and the motor nuclei of trigeminal. PONTINE Projections to the Involvement in RETICULAR intra-laminar and cardiac pressor and FORMATION dorsomedial n. of depressor responses A. GIGANTOCEL thalamus, the suggests a role in LULAR hypothalamus, blood pressure RETICULAR supramammillary regulation and NUCLEUS and lateral possibly a treatment B. PARAGIGANT mammillary nuclei, for hypertension. OCELLULAR the Also possible RETICULAR septum, the application for the NUCLEUS diagonal band, treatment of urinary C. RAPHE spinal cord, retention disorders, MAGNUS cerebellum, and in the management brainstem of pain. autonomic nuclei MEDIAL Projections to Treatment of motion VESTIBULAR oculomotor complex sickness. NUCLEUS and cervical spinal cord motor neurons. CEREBELLAR Projections only Potential treatment PURKINJE to deep cerebellar of movement CELLS nuclei. disorders, particularly those involving planned movements, or those involving abnormalities of gait or stance. SPINAL CORD Ascending dorsal Primary site for horn projections treatment of pain, to thalamus, and for possible brainstem anesthetic reticular applications. Also formation and possible therapies central gray. for spasticity and Ventral horn movement disorders. projections to skeletal and/or smooth muscle.

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What is claimed is:
 1. A method of obtaining a composition which comprises determining whether a chemical compound binds to a human 5-HT_(1F) receptor expressed on the surface of a mammalian cell comprising a vector adapted for expressing the receptor in the cell, and if the compound binds to the receptor, admixing the compound with a carrier, wherein the human 5-HT_(1F) receptor (a) has an amino acid sequence identical to the amino acid sequence shown in FIG. 1 (SEQ ID NO. 2) or (b) is encoded by a nucleic acid sequence identical to the receptor-encoding nucleic acid sequence contained in plasmid pMO5-hl16a (ATCC Accession No. 75175).
 2. A method of obtaining a composition which comprises determining whether a chemical compound binds to and activates a human 5-HT_(1F) receptor expressed on the surface of a mammalian cell, and if the compound binds to and activates the receptor, admixing the compound with a carrier, wherein the mammalian cell comprises a vector which expresses the receptor; wherein the human 5-HT_(1F) receptor (a) has an amino acid sequence identical to the amino acid sequence shown in FIG. 1 (SEQ ID NO. 2) or (b) is encoded by a nucleic acid whose sequence is identical to the receptor-encoding nucleic acid sequence contained in plasmid pMO5-hl16a (ATCC Accession No. 75175); and wherein activation of the human 5-HT_(1F) receptor is determined by measuring cAMP formation.
 3. A method of obtaining a composition which comprises determining whether a chemical compound binds to and prevents the activation of a human 5-HT_(1F) receptor expressed on the surface of a mammalian cell, and if the compound binds to and prevents the activation of the receptor, admixing the compound with a carrier, wherein the mammalian cell comprises a vector which expresses the receptor; wherein the human 5-HT_(1F) receptor (a) has an amino acid sequence identical to the amino acid sequence shown in FIG. 1 (SEQ ID NO. 2) or (b) is encoded by a nucleic acid whose sequence is identical to the receptor-encoding nucleic acid sequence contained in plasmid pMO5-hl16a (ATCC Accession No. 75175); and wherein activation of the human 5-HT_(1F) receptor is determined by measuring cAMP formation. 